For switch mode PSUs (which are usualy the biggest pain to design), TI has a switch mode design tool (WEBENCH) that is mostly what you are describing (you specify your constraints and it gives you a selection of designs, usually cheapest, most efficient, and smallest). It'll even let you download a CAD file with the schematic and layout, though I'm not sure if using it is completely seamless. Of course, it'll only suggest TI parts...